MOSCOW — Russia on Friday condemned a U.S. missile strike against Syrian government forces as an attack on its ally and said it was suspending an agreement to minimize the risk of in-flight incidents between U.S. and Russian aircraft operating over Syria.

Even as Russian officials expressed hope that the strike against Syrian President Bashad al-Assad’s forces would not lead to an irreversible breakdown in U.S. relations with Moscow, the Kremlin’s decision to suspend the 2015 memorandum of understanding on the air operations immediately raised tensions in the skies over Syria.

President Vladi­mir Putin’s spokesman said the risk of confrontation between aerial assets of the U.S.-led coalition and Russia has “significantly increased” after President Trump ordered the launch of 59 Tomahawk cruise missiles at a Syrian air base in retaliation for a chemical attack that killed scores of civilians.

Under the now-suspended pact, the two countries had traded information about flights by a U.S.-led coalition targeting the Islamic State and Russian planes operating in Syria in support of the Assad government. Moscow was taking its action, the Russian Defense Ministry said, because it sees the U.S. strike “as a grave violation of the memorandum.”

Putin’s spokesman, Dmitry Peskov, further claimed that the Syrian government had no chemical weapons and dismissed the Trump administration’s explanation as an excuse to enter the conflict.

“President Putin considers the American strikes against Syria an aggression against a sovereign government in violations of the norms of international law, and under a far-fetched pretext,” Peskov told reporters. “This step by Washington is causing significant damage to Russian-American relations, which are already in a deplorable state.”

“Of course, Syria is our ally, considering that we are helping the Syrian armed forces at the Syrian leadership's request,” Peskov said.

The strike creates the possibility of a direct confrontation with Russia, which has forces on the ground and advanced air-defense systems capable of shooting down U.S. aircraft and missiles.

The so-called "deconfliction" channel that Russia suspended was established in 2015 to prevent mishaps, including collisions, after Russia deployed aircraft to a base along Syria’s Mediterranean coastline and began carrying out strikes on behalf of the Syrian regime. It calls for a U.S. colonel at an air base in Qatar and a Russian colonel to man a phone hotline and inform each other of where their countries’ planes are flying.

The arrangement has been far from ideal, however, and U.S. military officials have called in recent months for an expansion of deconfliction talks as Russian and U.S. military aircraft fly in increasingly close quarters over Syrian cities such as Manbij.